1. Field of the Invention
This invention relates to television camera systems utilized in commercial aircraft, and more particularly to a multi-camera closed circuit television system used to provide video to existing passenger entertainment video systems in order to provide views of the environment outside of the aircraft.
2. Description of Related Art
The advent of on board television in commercial aircraft for entertainment purposes has provided the focus for a variety of entertainment options for the passengers. In addition to the ordinary availability of motion pictures, other alternatives such as news programs, videos and the like have been made available to the passenger for their viewing via selection from a variety of channels representing different video sources. Furthermore, on board video systems have been utilized to provide the passengers with important safety and emergency information as an adjunct to the normal pre-flight briefings provided by the flight attendants. In recent times, the use of on-board video displays has gone increasingly from a projection type television to individual viewing screens for the passengers, thus opening up the possibility of selection by the passenger from among a great number of possible entertainment sources. One additional source for such entertainment is a view of the outside environment through which the aircraft is flying.
The first use of such cameras in a commercial setting was on board wide body aircraft in approximately the 1980 time frame. Such systems included a camera mounted in the cockpit and provided the passengers with a view of the take-off and landing more or less over the captain's shoulder. This scenario produced two issues which eventually led to the removal of the cameras from the flight deck. The first problem arose because the camera was mounted on the aft wall looking forward through the cockpit window, and this scheme resulted in the camera looking from the low ambient light condition through a window into either a very high ambient light condition, or virtual darkness. The auto iris function of the cameras used was not capable of handling this wide dynamic lighting range, and as a result the camera provided images that blossomed the video signal past useable level. Another problem was, since the camera field of view included most crew activities within the cockpit, the flight crews looked upon such exposure as undesirable; the surveillance also created an area of possible liability for the company in the event that activities occurred within the cockpit which resulted in some safety of flight issue.
In a later prior art system, an exterior viewing television camera has been mounted aboard commercial aircraft, utilizing a fairly large window cut in the fuselage skin forward of the nose wheel on 747 type aircraft. The television cameras were mounted behind the window by means of structural modifications that provided shelving for the camera head units and the associated camera control units. Warm air was ducted into the area to provide defogging of the window during ascent and descent, and to keep the camera head and associated electronics ambient temperatures at a normal operating level. This provision was required for proper operation, since the units were installed in an unpressurized portion of the fuselage. Such a system had a number of operational problems. For instance, the mechanical installation provided access only through the nose wheel well, which resulted in high maintenance man-hour requirements in the event of any problems with the cameras. Also, the cameras were exposed to cycling through relatively low and high pressure as the aircraft climbed from sea level pressures to operating pressures at the flight levels. Thus, this type of system included a number of operational disadvantages which severely limited the uses of the system, both due to operational limitations and cost of maintenance. The present invention provides at least two sources of high quality video of the external environment of the aircraft while eliminating or substantially limiting the problems outlined above.